Safety controls for gaseous fuel burners



April 2, 1946. c. K. sTRoBEl. 2,397,704

SAFETY CONTROLS FOR GASEOUS FUEL BURNERS Filed OCT.. 2l, 1944 y INVENTOR H115 A'I'I'ORN EY Patented Apr. 2, 1946 Y UNITED sTATEs PATENT oFFlcE SAFETY CONTROLS FOR GASEOUS FUEL BURNERS Charles K. Strobel, Pittsurgh, Pa., assignor to Robertshaw Thermostat Company, Youngwood,A Pa., a corporation of Pennsylvania.

Application. October 21, 1944, Serial No. 559,801

7 claims. (cl. 15s-117s) This invention relates to ignition and safety connection with the accompanying drawing, control systems for fuel burners and, more parwherein:

ticularly, to electrically operated systems there- Fig. 1 is a schematic view of a safety control for. apparatus for a gaseous fuel burner embodying In my copending application, Serial No'. 460,456, 5 this invention; and

iiled October 1, 1942 and which has matured into Fig. 2 is a circuit diagram showing the elec- Patent No. 2,380,125 dated July 1'0, 1945, there is, trical connections at the start of operation of the disclosed an ignition and safety control system system.

wherein a pilot burner may be used for lighting Referring more particularly to the drawing, a the main burner after the main fuel supply valve l gaseous fuel burner Ill is shown in Fig. 1 as being is opened. In this prior application an automatic supplied with fuel by a, main fuel pipe I2. The safety valve is adapted to shut off the ow of fuel fuel supply is controlled by a main valve I4 which, to the main burner under certain conditions, but in this instance, is adapted for manual operation not to the pilot burner which is controlled solely but which may be arranged for thermostatic opby the main fuel valve. eration if desired. Interposed in the fuel supply In numerous instances, and particularly where pipe l2 between the main valve I4 and the burner expensive fuels are used, it is advantageous to y l0 is an electromagnetic or solenoid gas valve I 6 extinguish both the burners when the safety valve of any known type which may be arranged, as operates. Such 100 per cent shut-off is necesin this instance, to be opened when current of sary and is required for all gases heavier than sufficient energizing value is supplied to the sole- 'air. This can be accomplished in the system noid and closed by gravity upon a reduction of of the aforesaid disclosure in a simple manner by the current value thereto below holding value. connecting the fuel supply pipe for the pilot burn- A pilot burner I8 is provided for igniting the er to the outlet side of the safety valve. However, main burner I0 and is supplied with fuel from a .with'this alteration it is apparent that the fuel 25 conduit 20 connected to the main fuel pipe I2 becannot flow to the pilot burner unless the safety tween the main burner I0 and the electromagnetic valve has first opened. The time delay so envalve i6. It will be observed, therefore, that the forced between energizing of the igniter and iiow electromagnetic valve I6 controls the iiow of fuel of fuel therearound introduces objectionable feato both the main burner IIJ and the pilot Vburner tures which this invention seeks to overcome. I8. However, should the throttling of the pilot It has been found that with the system altered burner fuel be objectionable, the combined gas as described the useful life of the electric resistcock and thermostat arrangement could be placed ance igniter for the burner is greatly shortened. in the pipe'l2 between the main burner lo and the The operating conditions in thissystem are genconduit 2li. l

erally harmful to prolonged life of the resistance Electric current for the operation of the appaigniter. As'the usefulness of the entire system ratus is supplied by the line wires 22 connected to depends upon a proper functioning of the igniter, the primary of a transformer 26. It is sometimes it is 4apparent that the importance of arrangedesirable that the now of electric current be terments for extending the life thereof cannot be minated when the main valve i4 is closed to shut too greatly emphasized, 40 oi the supply of fuel to both the main and pilot An Object Of this DVGIXOH iS t0 Secure faVOlburners. However, for house heating applications able CQldtOnS in an and Safety Control the current ow may be controlled by a room tem., system for the life of the igniter element While pemture thermostat (not shown) which is not rscgbfhe desired Complete Shutoff 0f the 45 controlled in any way by the main fuel valve lli.

In this embodiment, a main switch for the electric `current from the transformer 2li is incorporated in the main fuel valve i4 with suitable arrangement for causing closure of the main switch whenythe main valve i4 is actuated to Another object of the invention is to accomplish a simplification of existing circuit arrangements while retaining the full advantages thereof.

Another object of the invention is to avoid an overload on the safety devices of the system.v

Another Object of the invention is to permit Ollell pOSitlOl'l. It Will be apparent that thlns Switch l ignition to occur under unusual conditions at the mlght be Connected in the Primary Clcult With* start of operation of the system. out disturbing the operation of the system, or Other objects and advantages will becomeapif the disclosed combination with a room .temparent from the followmg description taken in oli Deatul'e thermostat iS used, then the Switch ance in response thereto.

could be operated through a relay to avoid using large lead wires to the thermostat.

The electrical circuit for the safety control and ignition system gf this invention is shown more particularly in/Fig. 2 and includes the main switch of valve I4 -which has one terminal connected by a wire 26 to one terminal of the secondary of the transformer 24 and the other terminal thereof connected by a wire 28 to a-junc tion 30. The other terminal of the secondary of the transformer 24 is connected by a wire 32 to a junction 34. It may be noted that the vvarious electrically operated elements of 'the system are connected upon initial closure of the main switch of valve I4 in a bridge type of circuit. f

Connected to the junction 30 areseries'resistor 38, an electric resistance igniter 48 f or the-pilot burner |8 in the form of a coil of suitable wire, and the normally closed switch 42 of .a control relay having time delayed operation,. all of which form one arm of the aforesaid bridge circuit. I'hese elements are connected in series circuit which may be traced by the wirev 36 from junction 30 to the resistor 38, wire 44 connecting the resistor 38 to the electric resistance igniter 40 and a wire 46 connecting the igniter 130 to the switch 42 which is connected by a wire 48 to a junction 50. A wire 52 .extending from the junction 50 serves to connect one terminal of the electromagnetic valve I6 thereto, the other terminal of this valve being connected by a wire 54 to the junction 34. The electromagnetic valve I6 and the connections described thus form the second arm of the aforementioned bridge circuit.

Connected by a wire 56 to the junction 34 is a ballast resistor 58 which forms a control resistor for the electromagnetic valve I6 for reasons which will appear hereinafter. The ballast resistor 58 is preferably'in the form of a coil of wire of material having normally a relatively low resistance and a positive temperature coemcient of resistance and is thermally responsive to the passage of current therethrough. Primarily, however, this element is responsive to the heat of the flame of the pilot burner I8, to which it is exposed as shown in Fig. 1, and will vary in resist- The opposite end of the ballast resistor 58 is connected by a, wire 60 to a junction 62 and forms the third arm of the y aforementioned bridge circuit.

Connected by wire 64 to junction 62 is a second ballast resistor 66 which is also formed from a coil of wire having normally a relatively low resistance and a positive temperature coefcient of resistance. As indicated in Fig. 1, the second resistance element 66 is not, however, exposed to the flame of any burner and is adapted to vary its resistance only due to the passage of current therethrough. The opposite end of the ballast resistor 66 is connected by a wire 68 to the junction 30`and forms-the fourth arm of theaforementioned bridge circuit.

A cut-out 'l0 having one terminal thereof connected by a wire 12 to the junction 50 and the other terminal thereof connected by a wire 'I4 to the junction 62 is included in the circuit. Preferably, the cut-out V'Ill is of the thermal typey having time-lag operation for a purpose which will appear hereinafter. Such devices are constructed with predetermined time current characteristics and usually contain a, heater element in addition to and affecting a fusible member which opens the circuit by passage of over-current. 'I'he cutout IILI connected as described,` forms the detector arm of the bridge circuit.

'I'he control switch 42 is provided with an Aactuating coil '16 having one terminal thereof connected by-a wire 18 to the wire 32 and the other terminal thereof connected by a wire 80 to the wire 68. Preferably, the switch 42 has va delayed opening of eighteen seconds following closure of the mainswitch of valve vI4 and has an instantaneous closing upon opening of this switch. Switches of this type are well known to the art and may be in the form of the mercury tube switches disclosed in Patent No. 1,778,439 W. R. Walker, October 14, 1930 and Patent No. 2,224,873 C. H. Larson, December 17, 1940, among others, to which reference may be had for a fuller description.

As indicated by the broken lines, Fig. 1, the chamber 82 of an oven or like device is adapted to contain the main burner I 0, pilot burner Iii, electric resistance igniter 40 and ballast resistor 58. Both the igniter 40 and ballast resistor 58 are exposed to the fiame of the pilot burner i8 and the latter is arranged in proximity to the main burner I8 to serveits intended purpose of ual or thermostatic closing of the main switch of valve I4 is effective upon opening'of' this valve as described and permits fuel to ilow in the main .fuel pipe i2. The value of the current supplied to the electromagnetic valve i6 through the connections described is suiilcient during the rst eighteen seconds, following closure of the main switch of valve I4, to cause this valve to move to open position.

y Consequently, fuel is admitted to both the main burner I0 and the pilot burner I8 substantially simultaneously with energizetion of the igniter 40. The fuel flowing from the pilot burner I8 is ignited `by the igniter 4U and, in tum, ignites the fuel owing from the main burner l0. seconds of operation of the main switch of valve i4.

If the cut-out I8 is considered of negligible inipedance it is apparent that, during the eighteen seconds starting period, the circuit consists of two parallel meshes connected in series with the cuit shown in Fig. 2 receives current which is maintained below its steady state operating value at all times during the starting period due to the various arms of the bridge being in substantial balance.

At the end of eighteen seconds the delay period of the switch 42 is terminated and the igniter 40 becomes deenergized byopening of this switch.'

In effect,- this will cause a reduction in the value of the current owing through the coil of the electromagnetic valve I6 sufficient to cause this valve to close. However, the ballast resistor 56 has now become heated by the flame of the pilot burner I8 so that suicient current ilows through the coil of This operation occurs within a few the electromagnetic valve Il to maintain the valve in open position. The heating of the ballast resistor 58 therefore serves to raise the resistance of the shunt established thereby around the coil of the valve I6 and cut-out l0. This increase of resistance will compensate for the increase in total circuit resistance due to removal of the igniter 40 if the circuitconstants areeffective1y arranged. However, if at any time during operation of the apparatus, the flameof the pilot4 burner I8 should cease, then the resistance of the ballast resistor 58 will be reduced by cooling and the current to the valve I6 rendered insuiiicient to retain this valve in open position. Flow of fuel to both burners will then cease.

The electromagnetic valve i8 will also close in the event that the resistor 58 fails through fracture or other destructive means. 'I'his additional safety feature, disclosed as the cut-out 10, will operate on the increase in current through the electromagnetic valve circuit which would occur upon failure of the resistor 58. 'I'he time-lag in' corporated in the cut-out 10 renders it inoperable for the purpose described during that part ofthe starting period when the inrush current may be large.

Due to the provision for simultaneous energizing of the igniter 40 andA iiow of fuel therearound, the igniter life is not reduced even though a 100 percent shut-ofi' feature is included in the system. The circuit is made considerably simpler than those heretofore known by the provision for forced pick-up of the electromagnetic valve as soon as the main switch is operated.- 'I'his also eliminates any overload on the, cut-out at any time during normal operation.

The use of the single time delay switch does not reduce the igniter current by a circuit change until itis deenergized. This allows time for ignition even if there should be some delay in fuel flow at the start of operations. However, usually the fuel impinges on the igniter as soon as-it is energized so that the operating conditions for the igniter are generally in conformity with those which have been found to prolong igniter life.

It will be understood that various changes can be made in the arrangement and combination of parts and in the form of the elements herein disclosed Within the scope of the appended claims -Without departing from the spirit of the invention.

I claim:

l. An ignition and safety control system for fuel burners energizable from a source of current supply and comprising an electric igniter for the burner connected in a first arm of an electrical bridge circuit, a control device in'said first arm and operable after a time delay-following energization of said circuit for rendering said igniter inoperable, an electrically operable fuel control device for the burner in a second arm of said bridge and operable to supply fuel when current of sufficient value is supplied thereto, a pair of resistors in the third and fourth arms respectively of said y bridge, one of said resistors being exposed to a one resistor is heated.

2. An ignition and safety control-system for fuel burners energizable from a. source of current supply andcomprising an electric resistance igniter for the burner connected in a first arm `of an electrical bridgevcircuit, a control switch in said first arm and operable after a time delay following energization of said circuit to cause de-' energization of said igniter, an electrically operable ,fuel control device for the burner in a second armvofsaid bridge and operable to supply fuel whenicurrent of suiiicient value is supplied thereto, a pair of ballast resistors in the third and fourth farms one of which is exposed to a fiame at the burner for varying in its resistance when heated thereby, said variation in resistance causing variation in said current value, and

' means for connecting the opposite junctions of said first and' fourth arms and said second and third arms to the current source for energizing said igniter and supplying current of said sufficient value to said fuel control device, said current value being rendered insufficient upon operation of said yswitch unless said one resistor is heated.

3. An ignition and safety control system for fuel burners energizable from a source of current supply and having main and pilot burners, an electric resistance igniter for the pilot burner connected in a first arm of an electrical bridge circuit, a control switch in said first arm and operable after a time delay following energizetion ci' said circuit to cause deenergization of said igniter, an electrically operable fuel control device in a second arm of said bridge and controlling the fuel supply to both the main and pilot burners, said fuel being supplied when current of sufficient value is supplied to said device, a pair of ballast resistors in the third and fourth arms one of which is exposed to a flame at the pilot burner for varying in its resistance when heated thereby, said variation in resistance causing variation in said current value, and means for connecting the opposite junctions of said first and fourth arms and said second and third arms to the current source for energizing said igniter-and supplying current of said suiiicient value to said fuel control device, said current value being rehdered insufficient upon operation of said switch unless said one resistor is heated.

4. An ignition and safety control system for fuel burners energizable from a source of current supply and having main and pilot burners, an electric resistance igniter for the pilot'burner connected in a first arm of an electrical bridge circuit, a control switch in said first arm and operable after a time delay following energization of said circuit to cause deenergization of said igniter, an electrically operable fuel control device in a second arm of said bridge and controlling the fuel supply to both the main and pilot burners, said fuel being supplied when current of suflicient value is supplied to said device, a ball-ast resistor in a third arm of said bridge and being exposed to a flame at the pilotburner for increasing in resistance when heated thereby, a second ballast resistor ina fourth arm of said bridge and being adapted to increase in resistance when heated by passage of current therethrough, a thermal cut-out connected across the opposite junctions of said first and second arms and said third and fourth arms, said bridge being converted upon operation of said switch to a circuit containing the first said resistor in parallel with .oncl and third arms to the current source for energizing said igniter and supplying current of said suiiicient value to said device, said current value being rendered insufficient upon operation of said switch unless said first resistor is heated.

5. An ignition and safety, control system for fuel burners energizable from a source of current supply and comprising an electrically operable fuel control device movable between fuel ow permitting and preventing positions, switching means for controllingenergization of said fuel control device from the source and operative to cause said movement thereof, means responsive to a condition caused by combustion of the fuel and electrically connectedr to said fuel control device for reducing the current' value supplied thereto sufficiently to cause movement thereof to i dow preventing position in the absence of said combustion, an electric resistance igniter for the fuel, control means responsive to operation of said switching means for rendering said condition responsive means ineffective to cause said movement for a predetermined period during which said condition responsive means has time to become responsive, said control means comprising switch contacts adapted to be closed for establishing a circuit from the source including said fuel control device, said igniter, and said condi- 4 magnetic means for operating said control switch and connected to opposite junctions of said first and fourth arms and said second and third arms, and means for connecting said opposite junctions to the source for energizing said igniter and said electromagnetic means and for supplying current of said -sufcient value to said fuel control device,

' said current value being rendered insufcient tion responsive means of suilicient energizing s lvalue to cause said movement to fuel ow permitting position, and means eilective uponA expiration of said period to cause opening of said switch contacts for disconnecting said igniter and rendering said condition responsive means effective if combustion does not exist.

6. An ignition and safety control system for fuel burners energizable from a source of current supply and comprising an electric resistance igniter for the burner connected in a first arm of 'an electrical bridge circuit, a control switch in upon operation of said switch unless said one resistor is heated.

7. An ignition and safety control system for 4 fuel burners energizable from a source of current supply and comprising an electrically operable fuel control device movable between fuel flow permitting andpreventing positions, a main fuel, cock, switching means for controlling energization of said fuel control device from the source and operative when closed to cause said movement thereof to Ifuel flow permitting position, means for concurrently opening said mainA cause said movement fora predetermined period during which said condition responsive means has time to become responsive, said control means comprising switch contacts adapted to be closed for establishing a circuit from the source including said fuel control device, said igniter, and said condition responsive means of sufficient energizing value to cause said movement to fuel ilow y permitting position, means effective upon expiration of said period to cause openingv of said switch contacts for disconnecting said igniter and rendering said condition responsive means effective if combustion does not exist, and electromagnetic means in circuit with the source and said switching means for rendering said contact opening means effective. I

CHARLES K STROBEL. 

